When Ontario teenager Kaitlyn Terrana is having one of her episodes, she can sleep for 20 hours a day, 10 days at a time.

That's because Terrana has Kleine-Levin Syndrome -- sometimes dubbed the "Sleeping Beauty" disorder -- that causes her to sleep for long chunks of time, CBC reported.

"In the beginning of her episodes, she starts off being very, very tired. By late evening I can usually tell that, yes, she is starting an episode, because she doesn't talk, she doesn't converse with anybody," Terrana's mother, Kathy, told CBC. "It's not very nice to say, but it's almost like she's a walking zombie, because when they're in their episodes they can be walking around but they don't know what's going on around them. So there's no empathy, there's no feeling whatsoever. She's in a complete fog."

Kleine-Levin Syndrome is incredibly rare -- ABC News reported that only about 1,000 people have it in the entire world -- and it can also be hard to diagnose. In Terrana's case, CBC reported that a diagnosis for the condition didn't come until a year and a half after her first episode because there is no set test for the condition.

The condition is more common in boys than in girls -- with 70 percent of people who have the condition being male -- and the excessive sleep is often accompanied by symptoms of extreme food intake, an increased sex drive, hallucinations and feelings of being disoriented, according to the National Institute of Neurological Disorders and Stroke.

At the onset of an episode the patient becomes progressively drowsy and sleeps for most of the day and night (hypersomnolence), waking only to eat or go to the bathroom. When awake, the patient's whole demeanor is changed, often appearing "spacey" or childlike. When awake he experiences confusion, disorientation, complete lack of energy (lethargy), and lack of emotions (apathy).

There is no cure for the condition, but "watchful waiting" is generally advised, the National Institute of Neurological Disorders and Stroke reported. In some cases, drug treatments can actually make the condition worse.

Terrana is not the first teen to make headlines for Kleine-Levin Syndrome. Earlier this year, The Sun reported on the case of British teen Stacey Comerford, whose latest episode lasted two months.

"When she's in an episode, she might get up to go to the toilet or get a drink but she's not awake. I call it sleep mode," Comerford's mother, Bernie, told The Sun, adding that she feeds her when she's in this trance-like state. "When she wakes, she thinks it's the following day. She doesn't have any memory of it."